$128$ is what percent of $800$ ?
Answer: Having a percent of something means that you get that percent out of every $100$ We can set up a proportion to find out what percent of $800$ we need to take to get $128$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We are trying to find the ${\text{percent}}$ . Is $800$ the ${\text{part}}$ or the ${\text{whole}}$ The $800$ is the ${\text{whole}}$ . This means the ${\text{part}}$ is $128$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{128}}{{800}}$ If we divide the denominator of the fraction on the right by $8$ , it will be the same denominator of the fraction on the left. To keep things equal, let's also divide the numerator on the right by $8$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{128 \div 8}}{{800 \div 8}}$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{16}}{{100}}$ $ {\text{percent}} = {16}$ So $128$ is $16\%$ of $800$.